The invention relates to a filter for the filtration of compressed air and other compressed gases as well as air and liquids, including porous support-jackets between which a filter-element is located the filter-element being composed of several layers of varying porosity, with the finely porous layer being covered, at least on its surface facing the inlet side, of said filter assembly by a less finely porous layer.
The quality of compressed air is of great importance, especially for breweries and bottling plants. The ambient atmosphere contains, under normal conditions, up to 140 million of contaminant particles per m.sup.3. The contaminant particles include pollen, flower dust, mildew and wild yeast. These impurities are not retained by the suction filter of a compressor, since they are much too small. Their size is between 0.00001 and 0.002 mm. To this is added an atmospheric humidity of from 50 to 80%. In addition, the atmosphere is enriched during compression with the pressure from the compressor. For example, the initial volume is reduced to a fifth by compression to 4 bar. This means that a five-fold concentration results. This is also true of the oxygen content.
At constant temperatures of e.g. 30.degree. C. and 100% atmospheric humidity as well as the multiplied oxygen concentration, ideal conditions for the growth of micro-organisms are produced in compressed air lines and containers. This constitutes for breweries and bottling plants a high risk of infection or deterioration of taste.
In the case of so-called working atmosphere without special requirements for atmospheric sterility, oil-lubricated compressors also find frequent application. The compressed air then receives additional contamination from the lubricating oil. The lubricating oil is oxidised under the influence of the markedly increased oxygen content and of the compression temperature, which can reach up to 200.degree. C. and more in the compressor. The lubricating oil becomes strongly aggressive under these influences. This and the other impurities of the compressed air largely contribute to wear in all compressed air units.
As a result of extra-fine dispersion, the impurities form aerosols. This means that they remain suspended in the compressed air and diffuse throughout the whole compressed air system.
This can be counteracted only to a slight extent by conventional separation methods, such as centrifugal separation or separation with sinter-metal separators or ceramic separators.
Decisive criteria for the quality of a filter are its tool life and filtering action. The invention is based on the problem, therefore, of improving the tool life and filtering action.